Roaming method between wireless local area network and cellular network

ABSTRACT

The present invention relates to a roaming method between a WLAN and a cellular network which can interwork the WLAN and the cellular network on the basis of a mobile IP system for smooth roaming. In data communication in the WLAN and/or the cellular network using the mobile IP system, the roaming method between the WLAN and the cellular network includes a step wherein a packet data serving node of the cellular network which recognizes allocation of an IP address to a specific mobile terminal notifies information on a current access state of the mobile terminal to an access point managing means of the WLAN located in a current service area of the mobile terminal, a step wherein the access point managing means which the mobile terminal newly accesses requests address renewal to replace an address of the packet data serving node by its address, allocates an IP address to the mobile terminal according to the renewal result, and notifies it to the packet data serving node, and a step wherein the packet data serving node which receives the notification message from the access point managing means transmits data obtained during the roaming due to the movement to the access point managing node, whereby the roaming is performed from the cellular network to the WLAN. In the same manner, the roaming can be performed from the WLAN to the cellular network.

TECHNICAL FIELD

The present invention relates to a roaming method between a wirelesslocal area network (WLAN) and a cellular network, and in particular toan improved roaming method between a WLAN and a cellular network whichcan interwork the WLAN and the cellular network on the basis of a mobileIP system for smooth roaming.

BACKGROUND ART

In general, the WLAN service has been distributed in the country andabroad on the basis of IEEE 802.11b standard having a maximal data rateof 11 Mbps by using 2.4 GHz band frequencies. 802.1x is used for userauthentication, and standardization of 802.11i for security and 802.11efor quality of service are in progress.

Here, interworking of the WLAN and the cellular network must beconsidered in order to provide a flexible service by overcoming coveragelimits of an access point (AP). Accordingly, a lot of interests havebeen made on the activation of the WLAN service which has beendistributed worldwide and the interworking of the WLAN and cellularnetwork.

The most reliable method for interworking the WLAN and the cellularnetwork is to use a mobile IP. A general method using the mobile IPdisconnects a physical layer on a session and re-connects it. It takes afew seconds according to an existing protocol.

However, in order to provide a real time service such as image or voicecommunication, the disconnection and re-connection time must be reducedas much as possible. That is, when a terminal moves from one network toanother, a re-authentication and re-access process for the terminal mustbe performed in a short time. Therefore, there are strong demands for aroaming method between the WLAN and the cellular network which canreduce a time consumed to support mobility.

DISCLOSURE OF THE INVENTION

Accordingly, it is a primary object of the present invention to providea roaming method between a WLAN and a cellular network which can supportroaming suitable for a real time service by reducing a necessary timefor roaming, by rapidly supporting the roaming when a dual mode terminalwhich can access both the WLAN and the cellular network moves from aWLAN service area to a cellular service area or vice versa.

Another object of the present invention is to provide a roaming methodbetween a WLAN and a cellular network which can prevent data loss asmuch as possible during roaming because data maintenance is moreimportant in a data service than real time differently from a voiceservice.

That is, the present invention is intended to embody the roaming methodbetween the WLAN and the cellular network to minimize the data loss andreduce the time for roaming.

In order to achieve the above-described objects of the invention, indata communication in a WLAN and/or a cellular network using a mobile IPsystem, a roaming method between the WLAN and the cellular networkincludes a first step wherein a packet data serving node of the cellularnetwork which recognizes allocation of an IP address to a specificmobile terminal notifies information on a current access state of themobile terminal to an access point managing means of the WLAN located ina current service area of the mobile terminal, a second step wherein theaccess point managing means which the mobile terminal newly accessesrequests address renewal to replace an address of the packet dataserving node by its address, allocates an IP address to the mobileterminal according to the renewal result, and notifies it to the packetdata serving node, and a third step wherein the packet data serving nodewhich receives the notification message from the access point managingmeans transmits data obtained during the roaming due to the movement tothe access point managing node, whereby the roaming is performed fromthe cellular network to the WLAN.

According to another aspect of the invention, in data communication in aWLAN and/or a cellular network using a mobile IP system, a roamingmethod between the WLAN and the cellular network includes a first stepwherein an access point managing means of the WLAN which recognizesallocation of an IP address to a specific mobile terminal notifiesinformation on a current access state of the mobile terminal to a packetdata serving node of the cellular network located in a current servicearea of the mobile terminal, a second step wherein the packet dataserving node which the mobile terminal newly accesses requests addressrenewal to replace an address of the access point managing means by itsaddress, allocates an IP address to the mobile-terminal according to therenewal result, and notifies it to the access point managing means, anda third step wherein the access point managing means which receives thenotification message from the packet data serving node transmits dataobtained during the roaming due to the movement to the packet dataserving node, whereby the roaming is performed from the WLAN to thecellular network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart for explaining a concept of a mobile IP system forthe present invention;

FIG. 2 is a flowchart for explaining a concept when a WLAN interworkedwith a cellular network operated on the basis of the mobile IP of FIG. 1is individually operated;

FIG. 3 is a flowchart showing a network interworking method when roamingis performed from the cellular network of FIG. 1 to the WLAN of FIG. 2in a roaming method between the WLAN and the cellular network inaccordance with a preferred embodiment of the present invention;

FIG. 4 is a flowchart showing a network interworking method when roamingis performed from the WLAN of FIG. 2 to the cellular network of FIG. 1in the roaming method between the WLAN and the cellular network inaccordance with the preferred embodiment of the present invention;

FIG. 5 shows a format of a Con-Inform message generated and transmittedin FIGS. 3 and 4; and

FIG. 6 shows a format of a Con-Notify message generated and transmittedin FIGS. 3 and 4.

BEST MODE FOR CARRYING OUT THE INVENTION

A roaming method between a WLAN and a cellular network in accordancewith a preferred embodiment of the present invention will now bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a flowchart for explaining a concept of a mobile IP system forthe present invention. Referring to FIG. 1, packet data serving nodesPDSN1 and PDSN2 (110: 111 and 112) are nodes located in the cellularnetwork which is CDMA 2000 1× network for performing a packet dataswitching function. A home agent (HA) 120 is a location registrationmeans positioned in the network for registering location upon thelocation registration request of a mobile terminal (MT) 11 through thePDSN 110. Here, the HA 120 includes a plurality of IP address resources,links them to recognition information of the PDSN 110 and the MT 11 onthe basis of the location registration request message, dynamicallyallocates an IP address, and generates an address registration requestmessage, an address renewal request message and an address deleterequest message as address renewal messages for renewing the allocatedIP address. A domain name server (DNS) 130 is an address managing meansfor registering, renewing or deleting the address allocated to the MT 11on the basis of the address renewal message (namely, addressregistration request message, address renewal request message or addressdelete request message) from the HA 120.

The concept of the mobile IP system will now be explained with referenceto FIG. 1.

When the subscriber MT 11 having a specific host name (han) requestslocation registration to the HA 120 through the PDSN1 111 (S201 andS202), the HA 120 allocates one of the IP address resources (ipi) to thecorresponding MT 11 on the basis of the location registration requestmessage from the PDSN1 (S203), registers location by linking theallocated IP address resource ip1 to the host name han of the MT 11 andthe recognition information of the current access PDSN1 111 (S204), andrequests IP address registration of han:ip1 to the DNS 130 on the basisof the location registration request message (S205). The DNS 130registers han:ip1 upon the request (S206).

When the MT 11 accessing the PDSN1 111 and registering its location andIP address resource moves and requests location registration to the HA120 through the PDSN2 112 with its host name han and allocated IPaddress ip1 (S207 and S208), the HA 120 recognizes that the PDSN of theregistered han:ip1 is changed from the PDSN1 111 to the PDSN2 112 on thebasis of the location registration request message from the PDSN2 112,and registers location by linking han:ip1 to the recognition informationof the PDSN2 112 (S209).

The HA 120 allocates the IP address resource according to the locationregistration request message, registers the allocated IP address,confirms reception of the location registration request message for theregistered han:ip1, and calculates a non-reception time (S210). When thenon-reception time exceeds a predetermined time (S211), the HA 120requests deletion of the registered han:ip1 to the DNS 130 (S212). TheDNS 130 deletes the han:ip1 registration information on the basis of thedelete request message (S213), and notifies completion of the deletionto the HA 120 to dynamically allocate the allocated address resource ip1to another terminal (S214).

FIG. 2 is a flowchart for explaining a concept when the WLAN interworkedwith the cellular network operated on the basis of the mobile IP of FIG.1 is individually operated. In FIG. 2, reference numeral 12 denotes amobile terminal such as a notebook PC having a WLAN communicationfunction, reference numeral 20 denotes an access point which the mobileterminal 12 wirelessly accesses for communication, and reference numeral30 denotes an authentication/charging server for authentication andcharging during the data communication of the mobile terminal 12.

When the mobile terminal 12 accesses the access point 20 (S251), it isauthenticated according to 801.1x authentication procedure through theauthentication/charging server 30 (S252). Here, 802.1x is one of theexisting methods including MD-5, TLS, SRP and OTP.

After the authentication procedure is finished, the access point 20transmits a message Acc-Request(start) for notifying charging start tothe authentication/charging server 30 to start charging (S253), andprovides a data service to the mobile terminal 12 until the access isended in S251 (S254).

FIG. 3 is a flowchart showing a network interworking method when roamingis performed from the cellular network of FIG. 1 to the WLAN of FIG. 2in the roaming method between the WLAN and the cellular network inaccordance with the preferred embodiment of the present invention.

FIG. 4 is a flowchart showing a network interworking method when roamingis performed from the WLAN of FIG. 2 to the cellular network of FIG. 1in the roaming method between the WLAN and the cellular network inaccordance with the preferred embodiment of the present invention.

In the embodiment of FIGS. 3 and 4, the cellular network is a CDMA 20001× network, a base station controller (BSC) 410, a packet data servingnode (PDSN) 420 and a home agent (HA) 430 of FIG. 3 denote nodes of thecellular network of FIG. 1, and an access point (AP) 510 and an accesspoint managing device (APM) 520 denote nodes of the WLAN of FIG. 2. TheAPM 520 which is a node for managing the AP 510 and supporting mobilityis newly installed in the WLAN to have a function corresponding to thePDSN 420, and an authentication/charging server (AAA) 440 is a serverfor authenticating and charging users of the cellular network and theWLAN. In addition, a mobile terminal (MT) 10 is a dual mode terminalwhich can access both the cellular network of FIG. 1 and the WLAN ofFIG. 2, and embody a mobile IP stack. The PDSN 420 and the APM 520 areoperated as nodes for performing a mobile IP-based switching function ineach network in order to support mobility of the MT 10.

The roaming method from the cellular network to the WLAN will now beexplained with reference to FIG. 3.

The MT 10 located in the cellular network performs channel and R-P setupthrough the BSC 410 including the base station and the PDSN 420. Thatis, the MT 10 accesses the BSC 410 for performing mutual channel setup(CH setup) (S301), and the channel setup BSC 410 performs mutual R-Psetup with the PDSN 420 (S302), which has been disclosed in the priorart.

Thereafter, the MT 10 and the PDSN 420 perform point-to-point protocol(PPP) authentication (S303). Accordingly, the PDSN 420 transmits anaccess request respectively to the HA 430 and the AAA 440 and receivesresponses so that the HA 430 and the AAA 440 can perform relatedfunctions (S304). This procedure has also been disclosed in the priorart.

The mobile IP stack of the MT 10 performs a predetermined procedure withthe PDSN 420 to receive an IP address (MIP solicitation & advertisement)(S305).

After performing a protocol related with the mobile IP in S305, the MT10 requests location registration to the HA 430 through the PDSN 420 byusing a network access identifier (NAI), ID and password (RegistrationRequest) (S306 and S307). The HA 430 transmits an access request messageAccess Request to the AAA 440 to start charging (S308), and receives aresponse message Access Response (S309). As a result, when the userauthentication and mobile IP registration of the AAA 440 and the HA 430are successful, the HA 430 allocates the IP address to the MT 10 throughthe PDSN 420 and the BSC 410 as the response to S306 and S307 (S310 andS311). The procedure of S306 to S311, namely the procedure for thelocation registration and IP address allocation is identical to theprocedure of S201 to S206 except for the process related to the AAA 440,and thus detailed explanations thereof will be omitted.

The PDSN 420 which the MT 10 currently accesses detects the currentlocation of the MT 10 (namely, base station area) by S311 and theregistration response, and notifies the current access state of the MT10 to the APM 520 which is a managing device for the AP 510 in the areaby using a Con-Inform message as shown in FIG. 5 (S312).

Referring to FIG. 5, the Con-Inform message includes a protocol versionand its length (for example, 1 byte), a message identifier and itslength (for example, 2 bytes), a packet length and its length (forexample, 2 bytes), a sender IP address and its length, a client MACaddress and its length, a user ID and its length, a user NAI and itslength, a user password and its length, sequence numbers from 0 to 2048and its length (for example, 2 bytes), and others.

When the MT 10 moves to the WLAN area for access, it is authenticatedaccording to 802.1x through the AP 510 and the APM 520 (S313 and S314).Here, when the APM 520 receives the information on the MT 10 in S312, itrequests renewal of a binding table to the HA 430 by using its addressas a care of address (COA) (Roam Registration) (S315).

Thereafter, the APM 520 transmits the allocated IP address renewed inS315 to manage the MT 10 upon the request of the MT 10 (DHCP request &response) (S316). The address is necessary to transmit data from the APM520 to the MT 10.

The APM 520 notifies that roaming has been performed to the PDSN 420transmitting data in S312 by using a Con-Notify message as shown in FIG.6 (S317).

As shown in FIG. 6, the Con-Notify message includes a protocol versionand its length (for example, 1 byte), a message identifier and itslength (for example, 2 bytes), a packet length and its length (forexample, 2 bytes), a sender IP address and its length, a connectioncontext and its length, sequence numbers from 0 to 2048 and its length(for example, 2 bytes), and others.

Finally, the PDSN 420 receiving the Con-Notify message in S317 transmitsthe data obtained during the roaming to the APM 520 (Interval dataforwarding) (S318).

The roaming method from the WLAN to the cellular network will now beexplained with reference to FIG. 4.

The MT 10 located in the WLAN accesses the AP 510 (S601), and isauthenticated according to 801.1x authentication procedure through theAAA (S602).

The mobile IP stack of the MT 10 performs a predetermined procedure withthe APM 520 to receive an IP address (MIP solicitation andadvertisement) (S603).

After performing a protocol related with the mobile IP in S603, the MT10 requests location registration to the HA 430 through the APM 520 byusing an NAI value, ID and password (Registration Request) (S604 andS605). The HA 430 transmits an access request message Access Request tothe AAA 440 to start charging (S606), and receives a response messageAccess Response (S607). As a result, when the user authentication andmobile IP registration of the AAA 440 and the HA 430 are successful, theHA 430 allocates the IP address to the MT 10 through the APM 520 and theAP 510 as the response to S604 and S605 (S608 and S609).

The procedure of S604 to S609, namely the procedure for the locationregistration and IP address allocation is identical to the procedure ofS306 to S311. That is, the AP 510 and the APM 520 which areconstitutional nodes of the WLAN have similar/identical functions to thebase station/BSC 410 and the PDSN 420 which are constitutional nodes ofthe cellular network.

The APM 520 which the MT 10 currently accesses detects the currentlocation of the MT 10 (namely, AP area) by S609 and the registrationresponse, and notifies the current access state of the MT 10 to the PDSN420 for the base station/BSC 410 in the area by using the Con-Informmessage as shown in FIG. 5 (S610).

When the MT 10 moves to the cellular network area, the MT 10 located inthe cellular network performs channel setup and R-P setup through theBSC 410 and the PDSN 420 as in S301 to S303 of FIG. 3 (S611 and S612).Thereafter, the MT 10 and the PDSN 420 perform PPP authentication(S613).

Here, when the PDSN 420 receives the information on the MT 10 in S610,it requests renewal of a binding table to the HA 430 by using itsaddress as a COA (Roam Registration) (S614). It corresponds to S315 ofFIG. 3.

The PDSN 420 transmits the allocated IP address renewed in S614 tomanage the MT 10 upon the request of the MT 10 (DHCP request & response)(S615). The address is necessary to transmit data from the PDSN 420 tothe MT 10.

The PDSN 420 notifies that roaming has been performed to the APM 520transmitting data in S610 by using the Con-Notify message as shown inFIG. 6 (S616). Finally, the APM 520 receiving the Con-Notify message inS616 transmits the data obtained during the roaming to the PDSN 420(Interval data forwarding) (S617). The procedure of S615 to S617corresponds to the procedure of S316 to S318 of FIG. 3.

The aforementioned embodiment is not intended to be limiting. Forexample, the present invention can be used in 802.11a where a usingfrequency of the WLAN is 5 GHz band. That is, the present invention maybe embodied in several forms without departing from the spirit oressential characteristics thereof.

INDUSTRIAL APPLICABILITY

As discussed earlier, the roaming method between the WLAN and thecellular network can support roaming more suitable for the real timeservice by reducing the time for roaming, and prevent data loss duringthe roaming. That is, the present invention can minimize the data lossand reduce the time required for roaming.

1. In data communication in a WLAN and/or a cellular network using amobile IP system, a roaming method between the WLAN and the cellularnetwork, comprising: a first step wherein a packet data serving node ofthe cellular network which detects the current location of a specificmobile terminal provides a con-inform message to an access pointmanaging means associated with an access point of the WLAN located in acurrent service area of the mobile terminal, the con-inform messageincluding information on a current access state of the mobile terminal,wherein the access point managing means is notified of information on acurrent access state of the mobile terminal prior to the mobile terminalaccessing the access point; a second step wherein the access pointmanaging means associated with the access point which the mobileterminal newly accesses requests address renewal to replace an addressof the packet data serving node by its address, allocates an IP addressto the mobile terminal according to the renewal result, and provides acon-notify message to the packet data serving node the con-notifymessage including the IP address; and a third step wherein the packetdata serving node which receives the con-notify message from the accesspoint managing means transmits data obtained during the roaming due tothe movement to the access point managing means of the WLAN from thepacket data serving node of the cellular network, whereby the roaming isperformed from the cellular network to the WLAN.
 2. In datacommunication in a WLAN and/or a cellular network using a mobile IPsystem, a roaming method between the WLAN and the cellular network,comprising: a first step wherein an access point managing meansassociated with an access point of the WLAN which detects the currentlocation of a specific mobile terminal provides a con-inform message toa packet data serving node of the cellular network located in a currentservice area of the mobile terminal the con-inform message includinginformation on a current access state of the mobile terminal, whereinthe packet data servicing node is notified of information on a currentaccess state of the mobile terminal prior to the mobile terminalaccessing the packet data servicing node; a second step wherein thepacket data serving node which the mobile terminal newly accessesrequests address renewal to replace an address of the access pointmanaging means by its address, allocates an IP address to the mobileterminal according to the renewal result, and provides a con-notifymessage notifies it to the access point managing means, the con-notifymessage including the IP address; and a third step wherein the accesspoint managing means which receives the con-notify message from thepacket data serving node transmits data obtained during the roaming dueto the movement to the packet data serving node of the cellular networkfrom the access point managing means of the WLAN, whereby the roaming isperformed from the WLAN to the cellular network.
 3. The method of claim1, wherein the notification message of the first step includes aprotocol version and its length, a message identifier and its length, apacket length and its length, a sender IP address and its length, aclient MAC address and its length, a user ID and its length, a user NAIand its length, a user password and its length, sequence numbers and itslength.
 4. The method of claim 1, wherein the notification message ofthe second step includes a protocol version and its length, a messageidentifier and its length, a packet length and its length, a sender IPaddress and its length, a connection context and its length, sequencenumbers and its length.
 5. The method of claim 1, wherein the packetdata serving node and the access point managing means perform amobile-IP based switching function to support mobility of the mobileterminal.
 6. The method of claim 1, wherein the mobile terminal is adual mode terminal which can access both the cellular network and theWLAN and which embody a mobile IP stack.
 7. The method of claim 2,wherein the notification message of the first step includes a protocolversion and its length, a message identifier and its length, a packetlength and its length, a sender IP address and its length, a client MACaddress and its length, a user ID and its length, a user NM and itslength, a user password and its length, sequence numbers and its length.8. The method of claim 2, wherein the notification message of the secondstep includes a protocol version and its length, a message identifierand its length, a packet length and its length, a sender IP address andits length, a connection context and its length, sequence numbers andits length.
 9. The method of claim 2, wherein the packet data servingnode and the access point managing means perform a mobile-IP basedswitching function to support mobility of the mobile terminal.
 10. Themethod of claim 2, wherein the mobile terminal is a dual mode terminalwhich can access both the cellular network and the WLAN and which embodya mobile IP stack.